The placenta of the guinea-pig has assumed exceptional importance among the discoidal hemochorial placentae since the end of the sixties. Up to that date, numerous studies had been published on the functional analysis of the human placenta. One shortcom- ing common to all these studies, however, was the fact, that the human placenta was not absolutely suitable for morphological research, owing to fIxation difficulties, and for experimental investigations virtually unsuitable. Since other hemochorial villous placentae, like that of the anthropoid apes (primates) were practically unobtainable,...